Traditionally, in conventional processes for forming metal castings, a mold such as a metal die or sand mold having an interior chamber with the exterior features of a desired casting defined therein, is filled with a molten metal. A sand core that defines interior features of the casting is received and or positioned within the mold to form the interior detail of the casting as the molten metal solidifies about the core. After the molten metal of the casting has solidified, the casting generally is thereafter moved to a treatment furnace(s) for heat treatment of the castings, removal of sand from the sand cores and/or molds, and other processes as required. The heat treatment processes condition the metal or metal alloys of the castings so that they will be provided with desired physical characteristics suited for different applications.
Typically, during the transfer of the castings from the pouring station to a heat treatment station, and especially if the castings are allowed to sit for any appreciable amount of time, the castings are generally exposed to the ambient environment of the foundry or metal processing facility. As a result, the castings tend to begin to rapidly cool down from a molten or semi-molten temperature. While some cooling of the castings is necessary to cause the castings to solidify, the present inventors/applicants have found that the more that the temperature of the castings drops and the longer the castings remain below a process critical or process control temperature of the castings, the more heat treatment time within the heat treatment furnace that is required to both heat the castings back up to a desired heat treatment temperature and hold the castings at said temperature for heat treating the castings to achieve the desired physical properties thereof.
It has been found that for certain types of metals, for every minute of time that the casting drops below its process control temperature, as much as 4 minutes or more of extra heat treatment time is required to achieve the desired process. Thus, even dropping below for as little as ten minutes below the process control temperature of the metal of the castings can require as much as 40+ minutes of extra heat treatment time to achieve the desired treated physical properties. Typically, therefore, those castings are heat treated for at least 2-6 hours, and in some cases longer, to achieve the desired heat treatment effects. As a consequence, however, the longer the heat treatment time and the more heat required to properly and completely heat treat the castings, the greater the cost of the heat treatment process and the greater the waste of heat and energy.
Attempts have been made to shorten the distance between the pouring and heat treatment stations to try to reduce the loss of heat. For example, the Mercedes unit of Daimler Benz in Germany has placed a heat treatment furnace close to the take off or transfer points of a carousel type pouring station. As the castings reach a take-off point where they are removed from their dies, they generally are transported to a basket or carrier for collection of a batch of castings. The castings are then introduced into a heat treatment furnace for batch processing. The problem with this system is that it still fails to address the problem of the castings being subjected to the ambient environment, which generally is at temperatures much lower than the desired process control temperature of the castings, both during the transfer of the castings to a collection basket and while the castings sit in the basket awaiting introduction into the heat treatment furnace. This idle time can still be as much as 10 minutes or more depending upon the processing rates of the pouring and heat treatment stations. However, it is also important for the castings to be cooled and maintained at a temperature at or below the heat treatment temperature of the casting metal(s) for at least some desired time, in order to enable the castings to properly solidify prior to heat treatment. Thus, moving the castings from pouring to heat treatment too quickly can disrupt the formation of the castings and prevent them from properly solidifying.
There is, therefore, a desire in the industry to enhance the process of heat treating castings, such that a continuing need exists for a more efficient method and system or facility to enable more efficient heat treatment and processing of metal castings, and further potentially enable more efficient sand core and/or sand mold removal and reclamation.